Torsional Vibration Dampers (TVDs) are useful in attenuating torsional vibrations inherent to rotating shafts, including but not limited to crankshafts, drive-shafts, prop-shafts, and half-shafts utilized in automotive and non-automotive applications. Commonly, a TVD consists of three components: (1) a rigid metallic bracket (hub) attaching the TVD to the rotating shaft with the vibratory problem; (2) an active inertia member (ring) oscillating opposite in phase to the vibrating shaft at a particular frequency, thereby reducing the resulting magnitude of the shaft vibration; and (3) an elastomeric member (strip) with two functions: (a) providing a spring damper, thereby tuning the TVD to a particular frequency; and (b) locating the hub and the ring with respect to each other in the TVD.
The hub of a TVD consists of a central bore that connects the TVD to the vibratory shaft, an outer flange that provides a mating surface for the strip, and a plurality of spokes that connect the central bore to the outer flange. The hub of the damper is a structural bracket and its associated mass and inertia have no bearing on attenuating the vibration in the system. Spoke design is therefore a balance between giving the hub adequate structural strength and NVH stability and minimizing the amount of material used, thereby reducing the parasitic inertia and mass thereof. Two traditional styles of spokes are commonly employed in hub design—tapered rectangular beam and I-beam spokes.
The hub experiences a combination of alternating loads (once every revolution) such as belt forces and belt torques; and vibratory loads (multiple times every revolution when the damper is at resonance) such as the dynamic torque. However, in recent years with the development and usage of lighter and more flexible shafts, vibratory bending loads are sometimes encountered. When such vibratory bending loads come into play, the resulting spoke designs tend to be well-designed for one type of vibratory loading (usually bending) and over-designed for the other (usually torsion). This causes the spokes and consequently the hub to be heavier than necessary.